Used in some APIs but not likely by many deployers. One exception is the HttpClientSupport class which gets used in scripts to process response bodies, eg. in the HTTP data connector. To maintain compatibility, a stub with warnings was left behind.
Moved net.shibboleth.utilities.java.support.security → net.shibboleth.shared.security
Command line tool changes but those are captured in shell files we supply. The AccessControl interfaces move but I don’t expect deployers would have directly interacted with that service as an API. Various beans move but they’re system-defined in almost all cases. Biggest API ripple is the IdentifierGenerationStrategy stuff, but that’s unlikely to affect anybody but us and probably needs more work given the use of impl classes all over the code base.